U.S. patent number 6,311,555 [Application Number 09/442,596] was granted by the patent office on 2001-11-06 for angular rate producer with microelectromechanical system technology.
This patent grant is currently assigned to American GNC Corporation. Invention is credited to Ching-Fang Lin, Hiram McCall.
United States Patent |
6,311,555 |
McCall , et al. |
November 6, 2001 |
Angular rate producer with microelectromechanical system
technology
Abstract
An angular rate producer is provided for measuring vehicle
angular rate, wherein high performance dither drive signal
generation and angular sensing signal extracting means are provided
for hands-on vibrating type angular rate detecting units, including
tuning forks and vibrating strings to obtain highly accurate
angular rate signals. The angular rate producer includes an
vibrating type angular rate detecting unit for detecting angular
rate via Corilois Effect; an interfacing circuitry for converting
angular motion-induced signals from the vibrating type angular rate
detecting unit into angular rate signals and converting inertial
element dither motion signals from the vibrating type angular rate
detecting unit into processible inertial element dither motion
signals; and a digital processing system for locking the
high-quality factor frequency and amplitude of the vibrating
inertial elements in the vibrating type angular rate detecting unit
by means of providing an electronic energy including dither drive
signal for the vibrating type angular rate detecting unit using the
processible inertial element dither motion signals.
Inventors: |
McCall; Hiram (Chatsworth,
CA), Lin; Ching-Fang (Chatsworth, CA) |
Assignee: |
American GNC Corporation (Simi
Valley, CA)
|
Family
ID: |
26680537 |
Appl.
No.: |
09/442,596 |
Filed: |
November 17, 1999 |
Current U.S.
Class: |
73/488;
700/1 |
Current CPC
Class: |
G01C
19/5719 (20130101) |
Current International
Class: |
G01C
19/56 (20060101); G01P 015/00 (); G05B
015/00 () |
Field of
Search: |
;73/488,504.02,504.12,504.16 ;700/1,73,302,303,304 ;701/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moller; Richard A.
Attorney, Agent or Firm: Chan; Raymond Y. David and Raymond
Patent Group
Claims
What is claimed is:
1. An angular rate producer with microelectromechanical system
technology for measuring a vehicle angular rate, comprising:
an angular rate detecting unit receiving dither drive signal to
maintain an oscillation of at least one set of inertial element
with constant momentum and producing angular motion-induced signals
with respect to said vehicle angular rate and inertial element
dither motion signals;
an interfacing means for converting said angular motion-induced
signals from said angular rate detecting unit into consistent and
repeatable angular rate signals that are proportional to said
vehicle angular rate, and converting said inertial element dither
motion signals from said angular rate detecting unit into digital
element displacement signals with predetermined phase; and
a digital processing system for inputting said digital element
displacement signals for producing said dither drive signal for
locking high-quality factor frequency and amplitude of said
oscillating inertial element in said angular rate detecting
unit.
2. The angular rate producer, as recited in claim 1, wherein said
angular rate detecting unit is a vibrating type angular rate
detecting unit for detecting vehicle angular motions and outputting
said angular motion-induced signals which are voltages proportional
to angular rate and torque signals.
3. The angular rate producer, as recited in claim 1, wherein said
angular rate detecting unit is a vibrating type angular rate
detecting unit for detecting angular rate through Corilois
Effect.
4. The angular rate producer, as recited in claim 3, wherein said
vibrating type angular rate detecting unit receives dither drive
signal to keep said inertial elements oscillating; carrier
reference oscillation signals, including capacitive pickoff
excitation signals; and displacement restoring signals, including
electrostatic torque signals to maintain said inertial elements
without offset to obtain improved sensing performance.
5. The angular rate producer, as recited in claim 4, wherein said
vibrating type angular rate detecting unit detects angular motion
of a vehicle in accordance with dynamic theory, that is Coriolis
Effect, and outputs said angular motion-induced signals, including
rate displacement signals which may be modulated carrier reference
oscillation signals, and said inertial element dither motion
signals, including dither displacement signals.
6. The angular rate producer, as recited in claim 3, wherein said
angular rate detecting unit further includes an additional
self-torque loops to maintain said inertial elements without offset
to obtain improved sensing performance and receives said dither
drive signal to keep said inertial elements oscillating, and said
carrier reference oscillation signals, including capacitive pickoff
excitation signals.
7. The angular rate producer, as recited in claim 6, wherein said
vibrating type angular rate detecting unit detects angular motions
of a vehicle in accordance with a dynamic theory, that is Coriolis
Effect, and outputs torque signals, and said inertial element
dither motion signals, including dither displacement signals.
8. The angular rate producer, as recited in claim 1, 2 or 3,
wherein said digital processing system receives said digital
inertial element displacement signals with known phase from said
interfacing circuitry for finding frequencies which have highest
Quality Factor (Q) Values, locking said frequencies, and locking an
amplitude to produce said dither drive signal, including high
frequency sinusoidal signals with a precise amplitude, to said
angular rate detecting unit to keep said inertial elements
oscillating at a predetermined resonant frequency.
9. The angular rate producer, as recited in claim 1, 2 or 3,
wherein said interfacing means comprises an interfacing circuitry
which comprises:
an oscillator for providing reference pickoff signals;
a dither motion control circuitry for receiving said inertial
element dither motion signals from said vibrating type angular rate
detecting unit and said reference pickoff signals from said
oscillator, and producing said digital inertial element
displacement signals with known phase; and
an angle signal loop circuitry for receiving said angular
motion-induced signals from said vibrating type angular rate
detecting unit and said reference pickoff signals from said
oscillator, and transforming said angular motion-induced signals
into said angular rate signals.
10. The angular rate producer, as recited in claim 8, wherein said
interfacing means comprises an interfacing circuitry which
comprises:
an oscillator for providing reference pickoff signals;
a dither motion control circuitry for receiving said inertial
element dither motion signals from said vibrating type angular rate
detecting unit and said reference pickoff signals from said
oscillator, and producing said digital inertial element
displacement signals with known phase; and
an angle signal loop circuitry for receiving said angular
motion-induced signals from said vibrating type angular rate
detecting unit and said reference pickoff signals from said
oscillator, and transforming said angular motion-induced signals
into said angular rate signals.
11. The angular rate producer, as recited in claim 9, wherein said
angle rate signal loop circuitry comprises:
a high pass filter circuit, which is connected to said vibrating
type angular rate detecting unit, for receiving said angular
motion-induced signals and removing low frequency noise of said
angular motion-induced signals, which are AC voltage signals output
from vibrating type angular rate detecting unit, to form filtered
angular motion-induced signals;
a voltage amplifier circuit for amplifying said filtered angular
motion-induced signals to an extent of at least 100 milivolts to
form amplified angular motion-induced signals;
an amplifier and summer circuit for subtracting a difference
between said angle rates of said amplified angular motion-induced
signals to produce a differential angle rate signal;
a demodulator, which is connected to said amplifier and summer
circuit, for extracting an amplitude of said in-phase differential
angle rate signal from said differential angle rate signal and said
capacitive pickoff excitation signals from said oscillator; and
a low-pass filter, which connected to said demodulator, for
removing a high frequency noise of said amplitude signal of said
in-phase differential angle rate signal to form said angular rate
signal output.
12. The angular rate producer, as recited in claim 10, wherein said
angle rate signal loop circuitry comprises:
a high pass filter circuit, which is connected to said vibrating
type angular rate detecting unit, for receiving said angular
motion-induced signals and removing low frequency noise of said
angular motion-induced signals, which are AC voltage signals output
from vibrating type angular rate detecting unit, to form filtered
angular motion-induced signals;
a voltage amplifier circuit for amplifying said filtered angular
motion-induced signals to an extent of at least 100 milivolts to
form amplified angular motion-induced signals;
an amplifier and summer circuit for subtracting a difference
between said angle rates of said amplified angular motion-induced
signals to produce a differential angle rate signal;
a demodulator, which is connected to said amplifier and summer
circuit, for extracting an amplitude of said in-phase differential
angle rate signal from said differential angle rate signal and said
capacitive pickoff excitation signals from said oscillator; and
a low-pass filter, which connected to said demodulator, for
removing a high frequency noise of said amplitude signal of said
in-phase differential angle rate signal to form said angular rate
signal output.
13. The angular rate producer, as recited in claim 11, wherein said
angle rate signal loop circuitry further comprises an integrator
connected with said low-pass filter for integrating said angular
rate signal to form a displacement restoring signal, and a driver
amplifier connected to said integrator for amplifying said
displacement restoring signal to form a driving signal, including a
re-torque signal, to said vibrating type angular rate detecting
unit to maintain said inertial elements of said vibrating type
angular rate detecting unit without offset.
14. The angular rate producer, as recited in claim 12, wherein said
angle rate signal loop circuitry further comprises an integrator
connected with said low-pass filter for integrating said angular
rate signal to form a displacement restoring signal, and a driver
amplifier connected to said integrator for amplifying said
displacement restoring signal to form a driving signal, including a
re-torque signal, to said vibrating type angular rate detecting
unit to maintain said inertial elements of said vibrating type
angular rate detecting unit without offset.
15. The angular rate producer, as recited in claim 9, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
16. The angular rate producer, as recited in claim 10, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
17. The angular rate producer, as recited in claim 11, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
18. The angular rate producer, as recited in claim 12, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
19. The angular rate producer, as recited in claim 13, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
20. The angular rate producer, as recited in claim 14, wherein said
dither motion control circuitry further comprises:
a trans impedance amplifier circuit, which is connected to said
vibrating type angular rate detecting unit, for changing said
output impedance of said dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing said displacement between said
inertial elements and said anchor combs;
an amplifier and summer circuit, which is connected to said trans
impedance amplifier circuit, for amplifying said two dither
displacement signals for more than ten times and enhancing said
sensitivity for combining said two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual dither drive signal and
noise from said dither displacement differential signal to form a
filtered dither displacement differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said capacitive pickoff excitation signals
as phase reference signals from an oscillator and said filtered
dither displacement differential signal from said high-pass filter
and extracting said in-phase portion of said filtered dither
displacement differential signal to produce an inertial element
displacement signal with known phase;
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal; and
an analog/digital converter, which is connected to said low-pass
filter, for converting said low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
21. The angular rate producer, as recited in claim 1, wherein said
oscillation of said inertial elements residing inside said
vibrating type angular rate detecting unit is driven by a high
frequency sinusoidal signal with precise amplitude.
22. The angular rate producer, as recited in claim 20, wherein said
oscillation of said inertial elements residing inside said
vibrating type angular rate detecting unit is driven by a high
frequency sinusoidal signal with precise amplitude.
23. The angular rate producer, as recited in claim 20, wherein said
digitized low frequency inertial element displacement signal is
first represented in term of a spectral content thereof by using
discrete Fast Fourier Transform (FFT), which is an efficient
algorithm for computing discrete Fourier transform (DFT), which
dramatically reduces said computation load imposed by said DFT,
which is used to approximate said Fourier transform of a discrete
signal.
24. The angular rate producer, as recited in claim 23, wherein
after said digitized low frequency inertial element displacement
signals are represented in terms of their spectral content by using
discrete Fast Fourier Transform (FFT), Q (Quality Factor) Analysis
is applied to their spectral content to determine said frequency
with global maximal Q value which is a function of basic geometry,
material properties, and ambient operating conditions, said
vibration of said inertial elements of said vibrating type angular
rate detecting unit at said frequency with global maximal Q value
resulting in minimal power consumption and canceling terms that
affect said excited mode.
25. The angular rate producer, as recited in claim 24, further
comprising a phase-locked loop and D/A converter for controlling
and stabilizing said selected frequency and amplitude.
26. The angular rate producer, as recited in claim 16, wherein, in
order to find said frequencies having highest Quality Factor (Q)
values, said digital processing system includes:
a discrete Fast Fourier Transform (FFT) module, which is arranged
for transforming said digitized low frequency inertial element
displacement signal from said analog/digital converter of dither
motion control circuitry to form amplitude data with said frequency
spectrum of said input inertial element displacement signal;
a memory array of frequency and amplitude data module for receiving
said amplitude data with frequency spectrum to form an array of
amplitude data with frequency spectrum;
a maxima detection logic module for partitioning said frequency
spectrum from said array of said amplitude data with frequency into
plural spectrum segments, and choosing those frequencies with said
largest amplitudes in said local segments of said frequency
spectrum;
a Q analysis and selection logic module, which is adapted for
performing Q analysis on said chosen frequencies to select
frequency and amplitude by computing said ratio of
amplitude/bandwidth, wherein said range for computing bandwidth is
between +-1/2 of said peek for each maximum frequency point.
27. The angular rate producer, as recited in claim 18, wherein, in
order to find said frequencies having highest Quality Factor (Q)
values, said digital processing system includes:
a discrete Fast Fourier Transform (FFT) module, which is arranged
for transforming said digitized low frequency inertial element
displacement signal from said analog/digital converter of dither
motion control circuitry to form amplitude data with said frequency
spectrum of said input inertial element displacement signal;
a memory array of frequency and amplitude data module for receiving
said amplitude data with frequency spectrum to form an array of
amplitude data with frequency spectrum;
a maxima detection logic module for partitioning said frequency
spectrum from said array of said amplitude data with frequency into
plural spectrum segments, and choosing those frequencies with said
largest amplitudes in said local segments of said frequency
spectrum;
a Q analysis and selection logic module, which is adapted for
performing Q analysis on said chosen frequencies to select
frequency and amplitude by computing said ratio of
amplitude/bandwidth, wherein said range for computing bandwidth is
between +-1/2 of said peek for each maximum frequency point.
28. The angular rate producer, as recited in claim 20, wherein, in
order to find said frequencies having highest Quality Factor (Q)
values, said digital processing system includes:
a discrete Fast Fourier Transform (FFT) module, which is arranged
for transforming said digitized low frequency inertial element
displacement signal from said analog/digital converter of dither
motion control circuitry to form amplitude data with said frequency
spectrum of said input inertial element displacement signal;
a memory array of frequency and amplitude data module for receiving
said amplitude data with frequency spectrum to form an array of
amplitude data with frequency spectrum;
a maxima detection logic module for partitioning said frequency
spectrum from said array of said amplitude data with frequency into
plural spectrum segments, and choosing those frequencies with said
largest amplitudes in said local segments of said frequency
spectrum;
a Q analysis and selection logic module, which is adapted for
performing Q analysis on said chosen frequencies to select
frequency and amplitude by computing said ratio of
amplitude/bandwidth, wherein said range for computing bandwidth is
between +-1/2+L of said peek for each maximum frequency point.
29. The angular rate producer, as recited in claim 8, wherein said
digital processing system further includes a phase-lock loop to
reject noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
30. The angular rate producer, as recited in claim 26, wherein said
digital processing system further includes a phase-lock loop to
reject noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
31. The angular rate producer, as recited in claim 27, wherein said
digital processing system further includes a phase-lock loop to
reject noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
32. The angular rate producer, as recited in claim 28, wherein said
digital processing system further includes a phase-lock loop to
reject noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
33. The angular rate producer, as recited in claim 8, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
34. The angular rate producer, as recited in claim 26, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
35. The angular rate producer, as recited in claim 27, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
36. The angular rate producer, as recited in claim 28, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
37. The angular rate producer, as recited in claim 30, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
38. The angular rate producer, as recited in claim 31, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
39. The angular rate producer, as recited in claim 32, wherein said
digital processing system further includes a D/A converter for
processing said selected amplitude to form said dither drive signal
with correct amplitude, and an amplifier for generating and
amplifying said dither drive signal to said angular rate detecting
unit based on said dither drive signal with said selected frequency
and correct amplitude.
40. The angular rate producer, as recited in claim 13, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
41. The angular rate producer, as recited in claim 14, wherein said
angle rate signal loop circuitry firer comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
42. The angular rate producer, as recited in claim 19, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
43. The angular rate producer, as recited in claim 20, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
44. The angular rate producer, as recited in claim 23, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
45. The angular rate producer, as recited in claim 28, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
46. The angular rate producer, as recited in claim 32, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
47. The angular rate producer, as recited in claim 36, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
48. The angular rate producer, as recited in claim 39, wherein said
angle rate signal loop circuitry further comprises:
an amplifier and summer circuit, which is connected to a torque
amplifier of said vibrating type angular rate detecting unit, for
amplifying said torque signals and enhancing said sensitivity for
more than ten times;
a high-pass filter circuit, which is connected to said amplifier
and summer circuit, for removing residual drive signals and noise
from said torque signal to form a filtered torque drive
differential signal;
a demodulator circuit, which is connected to said high-pass filter
circuit, for receiving said carrier reference signals as phase
reference signals from said oscillator and said filtered torque
drive differential signal from said high-pass filter circuit, and
extracting said in-phase portion of said filtered torque drive
differential signal to produce an inertial element rotation rate
signal with known phase; and
a low-pass filter, which is connected to said demodulator circuit,
for removing high frequency noise from said inertial element
rotation signal input thereto to form a low frequency inertial
element rotation signal as output angular rate signals.
49. An angular rate producing process for measuring a vehicle
angular rate, comprising the steps of:
(a) receiving dither drive signal to maintain an oscillation of at
least one set of inertial elements in an angular rate detecting
unit with constant momentum, and producing angular motion-induced
signals with respect to said vehicle angular rate and inertial
element dither motion signals;
(b) converting said angular motion-induced signals from said
angular rate detecting unit in an interfacing circuitry into
consistent and repeatable angular rate signals that are
proportional to said vehicle angular rate, and converting said
inertial element dither motion signals from said angular rate
detecting unit in said interfacing circuitry into digital element
displacement signals with predetermined phase; and
(c) inputting said digital element displacement signals into a
digital processing system and producing said dither drive signal
for locking high-quality factor frequency and amplitude of said
oscillating inertial elements in said angular rate detecting
unit.
50. The angular rate producing process, as recited in claim 49,
wherein said angular rate detecting unit is a vibrating type
angular rate detecting unit for detecting vehicle angular motions
through Corilois Effect and outputting said angular motion-induced
signals which are voltage proportional to angular rate and torque
signals.
51. The angular rate producer, as recited in claim 50, wherein said
step (c) comprises the steps of:
(c-1) receiving said digital inertial element displacement signals
with known phase from said interfacing circuitry for finding
frequencies which have highest Quality Factor (Q) Values,
(c-2) locking said frequencies, and
(c-3) locking an amplitude to produce said dither drive signal,
including high frequency sinusoidal signals with a precise
amplitude, to said angular rate detecting unit to keep said
inertial elements oscillating at a predetermined resonant
frequency.
52. The angular rate producer, as recited in claim 50, wherein said
step (b) comprises the steps of:
(b-1) providing reference pickoff signals by an oscillator;
(b-2) receiving said inertial element dither motion signals from
said vibrating type angular rate detecting unit and said reference
pickoff signals from said oscillator in a dither motion control
circuitry and producing said digital inertial element displacement
signals with known phase; and
(b-3) receiving said angular motion-induced signals from said
vibrating type angular rate detecting unit and said reference
pickoff signals from said oscillator in an angle signal loop
circuitry, and transforming said angular motion-induced signals
into said angular rate signals.
53. The angular rate producer, as recited in claim 51, wherein said
step (b) comprises the steps of:
(b-1) providing reference pickoff signals by an oscillator;
(b-2) receiving said inertial element dither motion signals from
said vibrating type angular rate detecting unit and said reference
pickoff signals from said oscillator in a dither motion control
circuitry and producing said digital inertial element displacement
signals with known phase; and
(b-3) receiving said angular motion-induced signals from said
vibrating type angular rate detecting unit and said reference
pickoff signals from said oscillator in an angle signal loop
circuitry, and transforming said angular motion-induced signals
into said angular rate signals.
54. The angular rate producer, as recited in claim 53, wherein said
steps (b-3) further comprises the steps of:
(b-3-1) receiving said angular motion-induced signals by a
high-pass filter circuit connected to said vibrating type angular
rate detecting unit and removing low frequency noise of said
angular motion-induced signals, which are AC voltage signals output
from vibrating type angular rate detecting unit, to form filtered
angular motion-induced signals;
(b-3-2) amplifying said filtered angular motion-induced signals by
a voltage amplifier circuit to an extent of at least 100 milivolts
to form amplified angular motion-induced signals;
(b-3-3) subtracting a difference between said angle rates of said
amplified angular motion-induced signals in an amplifier and summer
circuit to produce a differential angle rate signal;
(b-3-4) extracting an amplitude of said in-phase differential angle
rate signal from said differential angle rate signal and said
capacitive pickoff excitation signals from said oscillator in a
demodulator which is connected to said amplifier and summer
circuit; and
(b-3-5) removing a high frequency noise of said amplitude signal of
said in-phase differential angle rate signal in a low-pass filter
connected to said demodulator to form said angular rate signal
output.
55. The angular rate producer, as recited in claim 54, wherein said
step (b-3) further comprises the steps of:
(b-3-6) integrating said angular rate signal by an integrator
connected with said low-pass filter to form a displacement
restoring signal, and
(b-3-7) amplifying said displacement restoring signal by a driver
amplifier connected to said integrator to form a driving signal,
including a re-torque signal, to said vibrating type angular rate
detecting unit to maintain said inertial elements of said vibrating
type angular rate detecting unit without offset.
56. The angular rate producing process, as recited in claim 53,
wherein said step (b-2) further comprises the steps of:
(b-2-1) changing said output impedance of said dither motion
signals from a very high level, greater than 100 million ohms, to a
low level, less than 100 ohms to achieve two dither displacement
signals, which are A/C voltage signals representing said
displacement between said inertial elements and said anchor
combs;
(b-2-2) amplifying said two dither displacement signals for more
than ten times and enhancing said sensitivity for combining said
two dither displacement signals to achieve a dither displacement
differential signal by subtracting a center anchor comb signal with
a side anchor comb signal;
(b-2-3) removing residual dither drive signal and noise from said
dither displacement differential signal to form a filtered dither
displacement differential signal;
(b-2-4) receiving said capacitive pickoff excitation signals as
phase reference signals from said oscillator and said filtered
dither displacement differential signal and extracting said
in-phase portion of said filtered dither displacement differential
signal to produce an inertial element displacement signal with
known phase;
(b-2-5) removing high frequency noise from said inertial element
displacement signal to form a low frequency inertial element
displacement signal; and
(b-2-6) converting said low frequency inertial element displacement
signal that is an analog signal to produce a digitized low
frequency inertial element displacement signal.
57. The angular rate producing process, as recited in claim 54,
wherein said step (b-2) further comprises the steps of:
(b-2-1) changing said output impedance of said dither motion
signals from a very high level, greater than 100 million ohms, to a
low level, less than 100 ohms to achieve two dither displacement
signals, which are A/C voltage signals representing said
displacement between said inertial elements and said anchor
combs;
(b-2-2) amplifying said two dither displacement signals for more
than ten times and enhancing said sensitivity for combining said
two dither displacement signals to achieve a dither displacement
differential signal by subtracting a center anchor comb signal with
a side anchor comb signal;
(b-2-3) removing residual dither drive signal and noise from said
dither displacement differential signal to form a filtered dither
displacement differential signal;
(b-2-4) receiving said capacitive pickoff excitation signals as
phase reference signals from said oscillator and said filtered
dither displacement differential signal and extracting said
in-phase portion of said filtered dither displacement differential
signal to produce an inertial element displacement signal with
known phase;
(b-2-5) removing high frequency noise from said inertial element
displacement signal to form a low frequency inertial element
displacement signal; and
(b-2-6) converting said low frequency inertial element displacement
signal that is an analog signal to produce a digitized low
frequency inertial element displacement signal.
58. The angular rate producing process, as recited in claim 55,
wherein said step (b-2) further comprises the steps of:
(b-2-1) changing said output impedance of said dither motion
signals from a very high level, greater than 100 million ohms, to a
low level, less than 100 ohms to achieve two dither displacement
signals, which are A/C voltage signals representing said
displacement between said inertial elements and said anchor
combs;
(b-2-2) amplifying said two dither displacement signals for more
than ten times and enhancing said sensitivity for combining said
two dither displacement signals to achieve a dither displacement
differential signal by subtracting a center anchor comb signal with
a side anchor comb signal;
(b-2-3) removing residual dither drive signal and noise from said
dither displacement differential signal to form a filtered dither
displacement differential signal;
(b-2-4) receiving said capacitive pickoff excitation signals as
phase reference signals from said oscillator and said filtered
dither displacement differential signal and extracting said
in-phase portion of said filtered dither displacement differential
signal to produce an inertial element displacement signal with
known phase;
(b-2-5) removing high frequency noise from said inertial element
displacement signal to form a low frequency inertial element
displacement signal; and
(b-2-6) converting said low frequency inertial element displacement
signal that is an analog signal to produce a digitized low
frequency inertial element displacement signal.
59. The angular rate producing process, as recited in claim 58,
wherein said digitized low frequency inertial element displacement
signal is first represented in term of a spectral content thereof
by using discrete Fast Fourier Transform (FFT), which is an
efficient algorithm for computing discrete Fourier transform (DFT),
which dramatically reduces said computation load imposed by said
DFT, which is used to approximate said Fourier transform of a
discrete signal.
60. The angular rate producing process, as recited in claim 59,
further comprising an additional step of controlling and
stabilizing said selected frequency and amplitude.
61. The angular rate producing process, as recited in claim 50,
wherein said step (c-1) further comprises the steps of:
(3-1-1) transforming said digitized low frequency inertial element
displacement signal from said analog/digital converter of dither
motion control circuitry to form amplitude data with said frequency
spectrum of said input inertial element displacement signal;
(3-1-2) receiving said amplitude data with frequency spectrum to
form an array of amplitude data with frequency spectrum;
(3-1-3) partitioning said frequency spectrum from said array of
said amplitude data with frequency into plural spectrum segments,
and choosing those frequencies with said largest amplitudes in said
local segments of said frequency spectrum;
(3-1-4) performing Q analysis on said chosen frequencies to select
frequency and amplitude by computing said ratio of
amplitude/bandwidth, wherein said range for computing bandwidth is
between +-1/2 of said peek for each maximum frequency point.
62. The angular rate producing process, as recited in claim 58,
wherein said step (c-1) further comprises the steps of:
(3-1-1) transforming said digitized low frequency inertial element
displacement signal from said analog/digital converter of dither
motion control circuitry to form amplitude data with said frequency
spectrum of said input inertial element displacement signal;
(3-1-2) receiving said amplitude data with frequency spectrum to
form an array of amplitude data with frequency spectrum;
(3-1-3) partitioning said frequency spectrum from said array of
said amplitude data with frequency into plural spectrum segments,
and choosing those frequencies with said largest amplitudes in said
local segments of said frequency spectrum;
(3-1-4) performing Q analysis on said chosen frequencies to select
frequency and amplitude by computing said ratio of
amplitude/bandwidth, wherein said range for computing bandwidth is
between +-1/2 of said peek for each maximum frequency point.
63. The angular rate producing process, as recited in claim 61,
wherein said step (3-2) further comprises the steps of (3-2-1)
rejecting noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
64. The angular rate producing process, as recited in claim 62,
wherein said step (3-2) further comprises the steps of (3-2-1)
rejecting noise of said selected frequency to form a dither drive
signal with said selected frequency by, which serves as a very
narrow bandpass filter.
65. The angular rate producing process, as recited in claim 61,
wherein said step (3-2) further comprises the steps of processing
said selected amplitude to form said dither drive signal with
correct amplitude, and generating and amplifying said dither drive
signal to said angular rate detecting unit based on said dither
drive signal with said selected frequency and correct
amplitude.
66. The angular rate producing process, as recited in claim 62,
wherein said step (3-2) further comprises the steps of processing
said selected amplitude to form said dither drive signal with
correct amplitude, and generating and amplifying said dither drive
signal to said angular rate detecting unit based on said dither
drive signal with said selected frequency and correct
amplitude.
67. The angular rate producing process, as recited in claim 63,
wherein said step (3-2) further comprises the steps of processing
said selected amplitude to form said dither drive signal with
correct amplitude, and generating and amplifying said dither drive
signal to said angular rate detecting unit based on said dither
drive signal with said selected frequency and correct
amplitude.
68. The angular rate producing process, as recited in claim 64,
wherein said step (3-2) further comprises the steps of processing
said selected amplitude to form said dither drive signal with
correct amplitude, and generating and amplifying said dither drive
signal to said angular rate detecting unit based on said dither
drive signal with said selected frequency and correct
amplitude.
69. The angular rate producing process, as recited in any of the
claims 56 to 68, wherein said step (2-2) further comprises the
steps of:
(b-2-7) amplifying said torque signals and enhancing said
sensitivity for more than ten times;
(b-2-8) removing residual drive signals and noise from said torque
signal to form a filtered torque drive differential signal;
(b-2-9) receiving said carrier reference signals as phase reference
signals from said oscillator and said filtered torque drive
differential signal, and extracting said in-phase portion of said
filtered torque drive differential signal to produce an inertial
element rotation rate signal with known phase; and
(b-2-10) removing high frequency noise from said inertial element
rotation signal to form a low frequency inertial element rotation
signal as output angular rate signals.
Description
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to an angular rate producer, and more
particularly to an angular rate producer with
microelectromechanical system (MEMS) technology to measure vehicle
angular rate. The angular rate producer of the present invention
comprises an vibrating type angular rate detecting unit, an
interfacing circuitry, and a digital processing system to obtain
more highly accurate, sensitive, stable vehicle angular rate
measurements under dynamic environments.
2. Description of Related Arts
Generally, an angular rate producer can function as an angular rate
sensor or a gyro. It can obtain vehicle angular rate measurements
to employ a conventional gyro in the vehicle. Many types of
approaches based on various sensing principles used to achieve an
angular rate sensor have been invented in the past decades, are
currently being invented, and will continue to be invented as
commercial markets for angular rate sensors continue to expand.
Existing angular rate sensors or gyros include spinning iron wheel
gyros and optical gyros.
Conventional spinning iron wheel gyros are principally based on the
Gyroscopic Law. The spinning iron wheel gyros generally have a
spinning wheel and analog output, high cost, were heavy, consumed a
lot of power because they had moving mechanical parts, and wore out
after just a few thousand hours of operation.
Existing optical gyros, including ring laser gyros and
interferometric fiber-optic gyros, are dependant on the Sagnac
Effect. The optical gyros generally have digital output and
moderate cost.
Truly low-cost, highly producible, miniaturized size, and low power
angular rate sensors with extended life have been a goal of the
industry for many years. Conventional angular rate sensors have
been commonly used in wide variety of applications. However, their
cost, size, and power prohibit them from the emerging commercial
applications, including phased array antennas.
Rapid advance in MEMS technologies makes it possible to fabricate a
low cost, light weight, miniaturized size, and low power angular
rate sensors. "MEMS" stands for "MicroElectroMechanical Systems",
or small integrated electrical/mechanical devices. MEMS devices
involve creating controllable mechanical and movable structures
using IC (Integrated Circuit) technologies. MEMS includes the
concepts of integration of Microelectronics and Micromachining.
Examples of successful MEMS devices include inkjet-printer
cartridges, accelerometers that deploy car airbags, and miniature
robots.
Microelectronics, the development of electronic circuitry on
silicon chips, is a very well developed and sophisticated
technology. Micromachining utilizes process technology developed by
the integrated circuit industry to fabricate tiny sensors and
actuators on silicon chips. In addition to shrinking the sensor
size by several orders of magnitude, integrated electronics can be
placed on the same chip, creating an entire system on a chip. This
instrument will result in, not only a revolution in conventional
military and commercial products, but also new commercial
applications that could not have existed without small, inexpensive
inertial sensors.
Some MEMS angular rate sensor approaches have been developed to
meet the need for inexpensive yet reliable angular rate sensors in
fields ranging from automotive to consumer electronics, based the
concept of using a vibrating element to sense angular rate under
the Coriolis principle. For example, single input axis MEMS angular
rate sensors are usually based on either translational resonance,
including tuning forks, or structural mode resonance, including
vibrating rings and associated microelectronic supporting
circuitry. Moreover, dual input axis MEMS angular rate sensors may
be based on angular resonance of a rotating rigid rotor suspended
by torsional springs. The inherent symmetry of the circular
configuration allows angular rate measurement about two axes
simultaneously.
Unfortunately, there is not a high performance commercial MEMS
angular rate sensors available, which can compete with the
measurement accuracy of conventional iron gyros and optical gyros.
It is still much more of a challenging to design and manufacture a
MEMS angular rate sensor with sufficient accuracy, keen
sensitivity, wide dynamic range, and high stability.
SUMMARY OF THE PRESENT INVENTION
A main objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate by obtaining highly
accurate angular rate signals. The high accuracy is obtained by
maximizing the device's momentum quality, or in other words,
selecting the momentum with the best combination of stability and
magnitude. The best momentum quality is obtained through high
performance dither drive signal generation and angular sensing
signal extracting means for hands-on vibrating type angular rate
detecting units, including tuning forks and vibrating strings.
Another objective of the present invention is to provide an angular
rate producer with microelectromechanical system (MEMS) technology
for measuring vehicle angular rate, which comprises:
a digital processing system for outputting dither drive energy
which is a kind of continuous or periodical electrical signal, such
as voltage, with predetermined frequency and amplitude;
an angular rate detecting unit for receiving the dither drive
energy to maintain a constant momentum of an oscillation of the
inertial element and producing an angular motion-induced signals
with a stable scale factor with respect to the vehicle angular rate
and inertial element dither motion signals; and
an interface means for transforming the angular motion-induced
signals received from the angular rate detecting unit into angular
rate signals adapted to be used and read by an inertial measurement
unit, outputting the angular rate signals, and converting the
inertial element dither motion signals to digital element
displacement signals with predetermined phase which are inputted
into the digital processing system for producing said dither
driving energy.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein the number
of resonance modes of the inertial elements of the vibrating type
angular rate detecting unit can be minimized by integrating the
interfacing circuitry and the digital processing system.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein the
interfacing circuitry and the digital processing system are
integrated to achieve resonance mode linearity of the inertial
elements of the vibrating type angular rate detecting unit.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein the
resonance modes of the inertial elements of the vibrating type
angular rate detecting unit is locked to increase the sensitivity
of the angular rate producer.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein the angular
rate bias and angular rate scale factor shift of the angular rate
producer is minimized.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein a closed
loop process for producer scale factor linearity can be
provided.
Another objective of the present invention is to provide an angular
rate producer employed with microelectromechanical system (MEMS)
technology for measuring vehicle angular rate, wherein the
interfacing circuitry and the digital processing system are
integrated to achieve displacement regulation of the inertial
elements of the vibrating type angular rate detecting unit for
angular rate producer scale factor stability, and temperature
stabilization for producer angular rate scale factor and angular
rate bias stability.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating the configuration of a
conventional micromachined sensor unit adapted to be used as a
vibrating type angular rate detecting unit.
FIG. 2 is a schematic view shows variable capacitive signal picking
off point connections for the micromachined sensor unit.
FIG. 3 is a block diagram of an angular rate producer according to
a preferred embodiment of the present invention.
FIG. 4 is a block diagram illustrated the vibrating type angular
rate detecting unit according to the above preferred embodiment of
the present invention.
FIG. 5 is a block diagram illustrated an alternative mode of the
vibrating type angular rate detecting unit according to the above
preferred embodiment of the present invention.
FIG. 6 is a block diagram of the interfacing circuitry according to
the above preferred embodiment of the present invention.
FIG. 7 is a block diagram of the angle signal loop circuitry
according to the above preferred embodiment of the present
invention.
FIG. 8 is a block diagram of the dither motion control circuitry
according to the above preferred embodiment of the present
invention.
FIG. 9 is a block the diagram of the digital processing system
according to the above preferred embodiment of the present
invention.
FIG. 10 is a block diagram of an alternative mode of the angle
signal loop circuitry adapted for the alternative mode of the
vibrating type angular rate detecting unit according to the above
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a preferred embodiment of the present
invention provides to an angular rate producer employed with
microelectromechanical system (MEMS) technologies for measuring
vehicle angular rate.
The angular rate producer of the present invention uses vibrating
inertial elements to sense vehicle angular rate via the Coriolis
Effect. The angular rate sensing principle of Coriolis Effect is
tie inspiration behind the practical vibrating angular rate
sensors.
The Coriolis Effect can be explained by saying that when an angular
rate is applied to a translating or vibrating inertial element, a
Coriolis force is generated. When this angular rate is applied to
the axis of an oscillating inertial element, its tines receive a
Coriolis force, which then produce torsional forces about the
sensor axis. These forces are proportional to the applied angular
rate, which then can be measured.
The force (or acceleration), Coriolis force (or Coriolis
acceleration) or Coriolis effect, is originally named from a French
physicist and mathematician, Gaspard de Coriolis (1792-1843), who
postulated his acceleration in 1835 as a correction for the earth's
rotation in ballistic trajectory calculations. The Coriolis
acceleration acts on a body that is moving around a point with a
fixed angular velocity and moving radially as well.
The basic equation defining Coriolis force can be expressed as
follows:
where
.omega. is the applied (input) angular rotation rate;
The Coriolis force produced is proportional to the product of the
mass of the inertial element, the input rotation rate, and
oscillation velocity of the inertial element that is perpendicular
to the input rotation rate.
Vibrating type angular rate detecting units using the Coriolis
effect can be designed and fabricated in different configurations.
An emerging advancement in fabricating a device used as a vibrating
type Coriolis Effect angular rate detecting unit is to fabricate a
micromachined unit functioning as a vibrating type angular rate
detecting unit on a chip using MicroelectronicMechanicalSystem
technologies. The typical available approaches, products, and
patents that can be used as vibrating type angular rate detecting
units are also diverse, including:
(A) Approaches:
Vibrating string;
Tuning fork;
Closed loop restore Quartz and silicon gyros;
Vibration angular and rotation Quartz and silicon gyros;
Bulk machined gyros;
Multi capacitive pickoff for detecting quartz resonance circular
mode vibrations.
(B) Products:
Systron Donner Quartz Rate Sensor(QRS);
Delco's Hemispherical Resonator gyro (HRG);
(C) U.S. Pat. Nos. and Titles:
1) U.S. Pat. No. 5,796,001, Monolithic micromechanical tuning fork
angular rate sensor
2) U.S. Pat. No. 5,767,405, Comb-drive micromechanical tuning fork
gyroscope with piezoelectric readout
3) U.S. Pat. No. 5,747,961, Beat frequency motor position detection
scheme for tuning fork gyroscope and other sensors
4) U.S. Pat. No. 5,635,639, Micromechanical tuning fork angular
rate sensor
5) U.S. Pat. No. 5,505,084, Micromechanical tuning fork angular
rate sensor
6) U.S. Pat. No. 5,496,436, Comb drive micromechanical tuning fork
gyro fabrication method
7) U.S. Pat. No. 5,492,596, Method of making a micromechanical
silicon-on-glass tuning fork gyroscope
8) U.S. Pat. No. 5,388,458, Quartz resonant gyroscope or quartz
resonant tuning fork gyroscope
9) U.S. Pat. No. 5,349,855, Comb drive micromechanical tuning fork
gyro
10) U.S. Pat. No. 5,952,574, Trenches to reduce charging effects
and to control out-of-plane sensitivities in tuning fork gyroscopes
and other sensors
11) U.S. Pat. No. 5,911,156, Split electrode to minimize charge
transients, motor amplitude mismatch errors, and sensitivity to
vertical translation in tuning fork gyros and other devices
12) U.S. Pat. No. 5,892,153, Guard bands which control out-of-plane
sensitivities in tuning fork gyroscopes and other sensors
In the present invention, the preferred vibrating type angular rate
detecting unit is a MEMS device, but not limited to MEMS device
obviously, because the MEMS technologies dramatically shrink the
size of a vibrating type angular rate detecting unit to the
microscopic level.
For instance, a configuration of such a Micromachined Sensor Unit
that can function as a vibrating type angular rate detecting unit
is shown in FIG. 1. In this configuration, the vibrating type
angular rate detecting unit detects angular rate by picking-off a
signal generated by an oscillating micromachined mass as it
deviates from its plane of oscillation under the Coriolis force
effect when the oscillating micromachined mass is submitted to a
rotation about an axis perpendicular to the plane of
oscillation.
Such micromachined sensor unit consists of two vibration devices
which have opposite dither motion directions. Thus, a pair of
differential measurements are formed to eliminate the effect of the
gravity and acceleration induced interference force. The inertial
elements are suspended by eight beams which also provide the
plastic force for the vibration at the same time. The beams are
attached to the substrate by anchors on the middle of the
beams.
Two vibrating inertial elements are attached by springs to each
other and to the surrounding stationary material. The vibrating
(dither) inertial elements are driven in opposite directions by
electrostatic comb drive motors to maintain lateral in-plane
oscillation. The dither motion is in the plane of the wafer. When
an angular rate is applied to the MEMS device about the input axis
(which is in the plane of the tines), the inertial elements are
caused to oscillate out of plane by a Coriolis force due to
Coriolis effect. The resulting out-of-plane oscillation motion
amplitude, proportional to the input angular rate, is detected and
measured by capacitive pickoff plates underneath the inertial
elements. The comb drives move the elements out of phase with
respect to each other. The elements will then respond in opposite
directions to the Coriolis force.
The circuitry detects this perpendicular motion by measuring the
change in capacitance. The sensitivity and stability of the device
is dependent on the amplitude of the dither motion, the frequency
of the oscillation, the mass of the device and the detection
method. The sensitivity is proportional to the product of the
velocity of the device and the angular rate. Maximizing the
amplitude and frequency of oscillation increases the sensitivity.
To increase the amplitude of oscillation, the device is run at the
resonant frequency of the supporting springs, which also minimizes
the energy required to drive the device. Typical resonant
frequencies are 1000-13,000 Hz.
The change in capacitance caused by the motion of the elements in
response to a Coriolis force is determined by measuring the current
flow from a high frequency signal (100 kHz to 1 MHz). The
capacitance is on the order of 0.5 pf with changes in capacitance
on the order of 1 ff. In order to achieve the greatest sensitivity,
the design of the configuration places the electronics as close as
possible to the pickoff electrodes on the device. This is done by
either integrating the electronics on the same wafer as the
micromachined sensor unit or by placing the electronics as close as
possible to the sensor package. On chip electronics can detect
changes in motion on the order of angstroms.
When an angular rate is applied about the angular rate input axis
of the micromachined sensor unit, the changed-capacitive signal can
be picked up.
FIG. 2 shows the capacitive pickoff configuration. Totally, six
capacitors are formed by the micromachined sensor unit structure.
Among them, four capacitors are formed by the two inertial elements
and three stators to construct four pairs of drive combs for the
vibration drive mechanism. Two capacitors are formed by two pairs
of inertial elements and sensor electrodes. When there is an
angular rate in the gyro input axis, one inertial element will move
towards its electrode and the other moves away from its electrode
under the Coriolis force. Thus the two sensor capacitors can be
used to form a differential measurement circuit.
Two techniques are presently employed to fabricate such a MEMS
device, bulk micromachining and surface micromachining. The
preferred MEMS fabrication of such a device is the surface
micromachining process. Surface micromachined devices are typically
a few microns to 10 microns thick. Angular rate sensors created
with surface machining have very low masses. The advantage of
surface machining is the low cost and the ease of incorporating the
electronics close to the sensor.
In surface micromachining, the inertial element is built onto the
surface of a silicon wafer. To build a surface micromachined
sensor, a few .mu.m thick layer of sacrificial oxide is deposited
on the passivation layer of a silicon wafer, in which n.sup.+ wells
have been previously diffused. Openings are then etched through
both insulators to the diffused areas in the substrate. A thick
layer of polysilicon is subsequently deposited over the entire
sensor area, filling the openings and establishing both a
mechanical and electrical bond with the n.sup.+ diffused areas. The
inertial elements are then etched into the layer of "floating"
polysilicon. The sacrificial oxide is subsequently removed from
under the polysilicon through further etching, leaving the
polysilicon layer essentially suspended in mid-air, yet still
attached to the substrate via the anchor posts, or pedestals,
formed at the points of diffusion.
The most commonly used surface micromachining processes starts with
silicon wafers of the same grade and type used in microelectronics
fabrication and uses layers of silicon dioxide as the sacrificial
material and layers of polysilicon, a deposited, less crystalline
form of silicon, as the structural material. Other deposited
materials including silicon nitride, polyimides, and aluminum are
also used to provide electrically insulating materials, conducting
materials, etchant masks, and additional structural materials. All
of these materials are extensively used and available in standard
microelectronics fabrication.
Because of the laminated structural and sacrificial material layers
and the etching of material done by a process that is insensitive
to crystalline structure, either because of the etch or because the
material itself is non-crystalline, surface micromachining enables
the fabrication of free form, complex, and multi-component
integrated MEMS structures, liberating the MEMS designer to
envision and build devices and systems that are impossible to
realize with bulk process. Surface micromachining also frees the
process developer and device designer to choose any material system
that has complementary structural and sacrificial materials. It is
this freedom to fabricate devices and systems without constraints
on materials, geometry, assembly and interconnections that is the
source for the richness and depth of MEMS applications that cut
across so many areas.
All actuation is done with electrostatic forces. These forces are
very weak so many obstacles can impede the motion of the inertial
elements. Problems can occur from dust or from the device not being
properly cleaned. The surface machined device is made by separating
all moving parts with a sacrificial oxide. The final step in the
processing is the removal of this oxide. Once the oxide is removed
the etching solution has to be completely removed with water and
then the water has to be removed with alcohol. The alcohol then has
to be removed completely by drying the device. If the solutions are
not removed by the correct process stiction occurs impeding the
motion of the device making it unusable. The device can also be
susceptible to the squeeze-film effect. If the device is run in
atmosphere the movement of the device can be impeded by the
inability of the trapped gas to move when the device moves. Many of
these devices are packaged in a vacuum environment. Getters are
usually employed in the package to maintain the quality of the
vacuum, although the use of a vacuum can degrade the device's
resistance to shock. Air damping increases shock resistance.
The major problems with micromachined vibrating type angular rate
sensors are insufficient accuracy, sensitivity, and stability.
Unlike MEMS accelerometers that are passive devices, micromachined
vibrating type angular rate sensors are active devices. Therefore,
associated high performance electronics and control should be
invented to effectively use hands-on micromachined vibrating type
angular rate sensors to achieve high performance angular rate
measurement in order to meet the requirement of being employed in
micro IMU.
Therefore, in order to obtain angular rate sensing signals from a
vibrating type angular rate detecting unit, a dither drive signal
or energy must be fed first to the vibrating type angular rate
detecting unit to drive and maintain the oscillation of the
inertial elements with a constant momentum. The performance of the
dither drive signals are critical for the whole performance of a
MEMS angular rate sensor.
The inertial elements are usually suspended electrostatically and
oscillate in a specific fashion. The dither drive signals are
generally sinusoidal signals with precise amplitude. The vibration
frequency and amplitude must be searched, selected, and locked by
an external device to make the vibrating type angular rate
detecting unit function under an optimal operational mode to obtain
improved angular rate sensing accuracy including more sensitivity
and more stability. Referring to FIG. 3, the producer of the
present invention comprises a vibrating type angular rate detecting
unit 10, an interfacing circuitry 20, and a digital processing
system 30.
The vibrating type angular rate detecting unit 10 is adapted for
detecting angular rate via Corilois Effect,
The interfacing circuitry 20 is adapted for converting angular
motion-induced signals from the vibrating type angular rate
detecting unit 10 into visible angular rate signals and converting
inertial element dither motion signals from the vibrating type
angular rate detecting unit 10 into processible inertial element
dither motion signals.
The digital processing system 30 is adapted for locking the
high-quality factor frequency and amplitude of the vibrating
inertial elements in the vibrating type angular rate detecting unit
10 by means of providing electrical energy including dither drive
signals for the vibrating type angular rate detecting unit 10 using
the processible inertial element dither motion signals.
Angular rate detecting unit 10 is a vibratory device, which
comprises at least one set of vibrating inertial elements,
including tuning forks, and associated supporting structures and
means, including capacitive readout means, and uses Coriolis
effects to detect vehicle angular rate.
Referring to FIG. 4, the first preferred mode of a vibrating type
angular rate detecting unit 10 receives signals as follows:
1) dither drive signals to keep the inertial elements
oscillating;
2) carrier reference oscillation signals, including capacitive
pickoff excitation signals; and
3) displacement restoring signals, including electrostatic torque
signals to maintain its inertial elements without offset to obtain
improved sensing performance.
The first preferred mode of the vibrating type angular rate
detecting unit 10 detects the angular motion of a vehicle in
accordance with the dynamic theory (Coriolis force), and outputs
signals as follows:
1) angular motion-induced signals, including rate displacement
signals which may be modulated carrier reference oscillation
signals; and
2) its inertial element dither motion signals, including dither
displacement signals.
Referring to FIG. 5, the second preferred mode of a vibrating type
angular rate detecting unit 10 includes the first preferred
vibrating type angular rate detecting unit 10 itself and additional
self-torque loops to maintain its inertial elements without offset
to obtain improved sensing performance and receives signals as
follows:
1) dither drive signals to keep the inertial elements oscillating;
and
2) carrier reference oscillation signals, including capacitive
pickoff excitation signals.
The second preferred mode of the vibrating type angular rate
detecting unit 10 detects the angular motion of a vehicle in
accordance with the dynamic theory (Coriolis force), and outputs
signals as follows:
1) torque signals; and
2) its inertial element dither motion signals, including dither
displacement signals.
According to the present invention, the vibrating type angular rate
detecting unit 10 detects vehicle angular motion and outputs
angular motion-induced signals, including AC or DC voltage
proportional to the angular rate and torque signals, and its
inertial element dither motion signals.
The interfacing circuitry 20 converts the angular motion-induced
signals into angular rate signals, for example, demodulating the AC
voltage into DC voltage proportional to the input angular rate,
produces digital inertial element displacement signals with known
phase using the inertial element dither motion signals from the
vibrating type angular rate detecting unit 10 to a digital
processing system 30.
The digital processing system 30 receives digital inertial element
displacement signals with known phase from the interfacing
circuitry 20 and performs the following:
3.1) finding the frequencies which have highest Quality Factor (Q)
Values,
3.2) locking the frequency, and
3.3) locking the amplitude to produce a dither drive signal,
including high frequency sinusoidal signals with a precise
amplitude, to the vibrating type angular rate detecting unit 10 to
keep the inertial elements oscillating at the pre-determined
resonant frequency.
Referring to FIG. 6, the interfacing circuitry 20 comprises a
dither motion control circuitry 21, an angle signal loop circuitry
22 and an oscillator 23.
The dither motion control circuitry 21 receives the inertial
element dither motion signals from vibrating type angular rate
detecting unit 10 and reference pickoff signals from an oscillator
23, and produces digital inertial element displacement signals with
known phase.
The angle signal loop circuitry receives the angular motion-induced
signals from the vibrating type angular rate detecting unit 10 and
reference pickoff signals from oscillator 23, and transforms the
angular motion-induced signals into angular rate signals.
The oscillator 23 provides reference pickoff signals for vibrating
type angular rate detecting unit 10, dither motion control
circuitry 21, and angle signal loop circuitry 22.
Referring to FIG. 7, the angle rate signal loop circuitry 22
comprises a high-pass filter circuit 2201, a voltage amplifier
circuit 2205, an amplifier and summer circuit 2210, a demodulator
2215, and a low-pass filter 2220.
The high pass filter circuit 2210 is connected to the vibrating
type angular rate detecting unit 10 for receiving the angular
motion-induced signals by a high-pass filter circuit 2201 and
removing low frequency noise of the angular motion-induced signals,
which are AC voltage signals output from vibrating type angular
rate detecting unit 10, to form filtered angular motion-induced
signals;
The voltage amplifier circuit 2205 amplifies the filtered angular
motion-induced signals to an extent of at least 100 milivolts to
form amplified angular motion-induced signals.
The amplifier and summer circuit 2210 subtracts the difference
between the angle rates of the amplified angular motion-induced
signals to produce a differential angle rate signal.
The demodulator 2215, which is connected to the amplifier and
summer circuit 2210, extracts the amplitude of the in-phase
differential angle rate signal from the differential angle rate
signal and the capacitive pickoff excitation signals from the
oscillator 23.
The low-pass filter 2220, which is connected to the demodulator
2215, removes the high frequency noise of the amplitude signal of
the in-phase differential angle rate signal to form the angular
rate signal output.
In order to obtain improved performance, including scale factor
linearity, the angle rate signal loop circuitry 22 further
comprises an integrator 2225 connected with the low-pass filter
2220 for integrating the angular rate signal to form a displacement
restoring signal, and a driver amplifier 2230 connected to the
integrator 2225 for amplifying the displacement restoring signal to
form a driving signal, including a retorque signal, to the
vibrating type angular rate detecting unit 10 to maintain the
inertial elements of the vibrating type angular rate detecting unit
10 without offset.
In order to convert the inertial element dither motion signals from
the vibrating type angular rate detecting unit 10 to processible
inertial element dither motion signals, referring to FIG. 8, the
dither motion control circuitry 21 further comprises a trans
impedance amplifier circuit 2105, an amplifier and summer circuit
2110, a high-pass filter circuit 2115, a demodulator circuit 2120,
a low-pass filter 2125, and an analog/digital converter 2130.
The trans impedance amplifier circuit 2105 is connected to the
vibrating type angular rate detecting unit 10 for changing the
output impedance of the dither motion signals from a very high
level, greater than 100 million ohms, to a low level, less than 100
ohms to achieve two dither displacement signals, which are A/C
voltage signals representing the displacement between the inertial
elements and the anchor combs.
The amplifier and summer circuit 2110 is connected to the trans
impedance amplifier circuit 2105 for amplifying the two dither
displacement signals for more than ten times and enhancing the
sensitivity for combining the two dither displacement signals to
achieve a dither displacement differential signal by subtracting a
center anchor comb signal with a side anchor comb signal.
The high-pass filter circuit 2115 is connected to the amplifier and
summer circuit 2110 for removing residual dither drive signals and
noise from the dither displacement differential signal to form a
filtered dither displacement differential signal.
The demodulator circuit 2120 is connected to the high-pass filter
circuit 2115 for receiving the capacitive pickoff excitation
signals as phase reference signals from an oscillator 23 and the
filtered dither displacement differential signal from the high-pass
filter 2115 and extracting the in-phase portion of the filtered
dither displacement differential signal to produce an inertial
element displacement signal with known phase.
The low-pass filter 2125 is connected to the demodulator circuit
2120 for removing high frequency noise from the inertial element
displacement signal input thereto to form a low frequency inertial
element displacement signal.
The analog/digital converter 2130 is connected to the low-pass
filter 2125 for converting the low frequency inertial element
displacement signal that is an analog signal to produce a digitized
low frequency inertial element displacement signal.
The oscillation of the inertial elements residing inside the
vibrating type angular rate detecting unit 10 is generally driven
by a high frequency sinusoidal signal with precise amplitude. It is
critical to provide the vibrating type angular rate detecting unit
10 with high performance dither drive signals to achieve keen
sensitivity and stability of angular rate measurements.
The digital processing system 30 is to search and lock the
vibrating frequency and amplitude of the inertial elements of the
vibrating type angular rate detecting unit 10.
Therefore, the digitized low frequency inertial element
displacement signal is first represented in term of their spectral
content by using discrete Fast Fourier Transform (FFT).
Discrete Fast Fourier Transform (FFT) is an efficient algorithm for
computing discrete Fourier transform (DFT), which dramatically
reduces the computation load imposed by the DFT. The DFT is used to
approximate the Fourier transform of a discrete signal. The Fourier
transform, or spectrum, of a continuous signal is defined as:
##EQU1##
The DFT of N samples of a discrete signals X(nT) is given by:
##EQU2##
where .omega.=2.pi./NT, T is the inter-sample time interval. The
basic property of FFT is its ability to distinguish waves of
different frequencies that have been additively combined.
After the digitized low frequency inertial element displacement
signals are represented in terms of their spectral content by using
discrete Fast Fourier Transform (FFT), Q (Quality Factor) Analysis
is applied to their spectral content to determine the frequency
with global maximal Q value. The vibration of the inertial elements
of the vibrating type angular rate detecting unit 10 at the
frequency with global maximal Q value can result in minimal power
consumption and cancel many of the terms that affect the excited
mode. The Q value is a function of basic geometry, material
properties, and ambient operating conditions.
A phase-locked loop and D/A converter is further used to control
and stabilize the selected frequency and amplitude.
Referring to FIG. 9, the digital processing system 30 further
includes a discrete Fast Fourier Transform (FFT) module 3005, a
memory array of frequency and amplitude data module 3010, a maxima
detection logic module 3015, and a Q analysis and selection logic
module 3020 to complete the above step 3.1 of finding the
frequencies which have highest Quality Factor (Q) Values.
The discrete Fast Fourier Transform (FFT) module 3005 is arranged
for transforming the digitized low frequency inertial element
displacement signal from the analog/digital converter 2130 of
dither motion control circuitry 21 to form amplitude data with the
frequency spectrum of the input inertial element displacement
signal.
The memory array of frequency and amplitude data module 3010
receives the amplitude data with frequency spectrum to form an
array of amplitude data with frequency spectrum.
The maxima detection logic module 3015 is adapted for partitioning
the frequency spectrum from the array of the amplitude data with
frequency into plural spectrum segments, and choosing those
frequencies with the largest amplitudes in the local segments of
the frequency spectrum.
The Q analysis and selection logic module 3020 is adapted for
performing Q analysis on the chosen frequencies to select frequency
and amplitude by computing the ratio of amplitude/bandwidth,
wherein the range for computing bandwidth is between +-1/2 of the
peek for each maximum frequency point.
Moreover, the digital processing system 30 further includes a
phase-lock loop 3025 to reject noise of the selected frequency to
form a dither drive signal with the selected frequency by, which
serves as a very narrow bandpass filter, during the above step 3.2
of locking the frequency.
The digital processing system 30 further includes a D/A converter
3030 and an amplifier 3035 to process the above step 3.3, wherein
the D/A converter 3030 processes the selected amplitude to form a
dither drive signal with correct amplitude and the amplifier 3035
generates and amplifies the dither drive signal to the vibrating
type angular rate detecting unit 10 based on the dither drive
signal with the selected frequency and correct amplitude.
In order to process the torque signals from the second preferred
vibrating type angular rate detecting unit 10, referring to FIG. 5
and FIG. 10, the angle rate signal loop circuitry 22 further
comprises:
an amplifier and summer circuit 2250, which is connected to a
torque amplifier of the vibrating type angular rate detecting unit
10, for amplifying the torque signals and enhancing the sensitivity
for more than ten times;
a high-pass filter circuit 2255, which is connected to the
amplifier and summer circuit 2250, for removing residual drive
signals and noise from the torque signal to form a filtered torque
drive differential signal;
a demodulator circuit 2260, which is connected to the high-pass
filter circuit 2255, for receiving the carrier reference signals as
phase reference signals from the oscillator 23 and the filtered
torque drive differential signal from the high-pass filter circuit
2255, and extracting the in-phase portion of the filtered torque
drive differential signal to produce an inertial element rotation
rate signal with known phase; and
a low-pass filter 2265, which is connected to the demodulator
circuit 2260, for removing high frequency noise from the inertial
element rotation signal input thereto to form a low frequency
inertial element rotation signal as output angular rate
signals.
In view of above, when the angular rate producer of the present
invention is employed to produce a kind of micro IMU, such micro
IMU can achieve the following unique features:
(1) Attitude Heading Reference System (AHRS) Capable Core Sensor
Module.
(2) Miniaturized (Length/Width/Height) and Light Weight.
(3) High Performance and Low Cost.
(4) Low Power Dissipation.
(5) Dramatic Improvement In Reliability (microelectromechanical
systems--MEMS).
Moreover, if such a micro IMU employed with the angular rate
producer of the present invention is utilized to produce an
integrated micro land navigator, it can achieve the following
unique features:
(1) Miniature, light weight, low power, low cost.
(2) AHRS, odometer, integrated GPS chipset and flux valve.
(3) Integration filter for sensor data fusion and zero velocity
updating.
(4) Typical applications: automobiles, railway vehicles, miniature
land vehicles, robots, unmanned ground vehicles, personal
navigators, and military land vehicles.
Also, when such a micro IMU employed with the angular rate producer
of the present invention is functioned as aircraft inertial
avionics, it can achieve the following unique features:
(1) Rate Gyro
(2) Vertical Gyro
(3) Directional Gyro
(4) AHRS
(5) IMU
(6) Inertial Navigation System
(7) Fully-Coupled GPS/MEMS IMU Integrated System
(8) Fully-Coupled GPS/IMU/Radar Altimeter Integrated System
(9) Universal vehicle navigation and control box.
Besides the angular rate producer of the present invention also
enables the micro IMU to be a Spaceborne MEMS IMU Attitude
Determination System and a Spaceborne Fully-Coupled GPS/MEMS IMU
Integrated system for orbit determination, attitude control,
payload pointing, and formation flight, which has the following
unique features:
(1) Shock resistant and vibration tolerant
(2) High anti-jamming
(3) High dynamic performance
(4) Broad operating range of temperatures
(5) High resolution
(6) Compact, low power and light weight unit
(7) Flexible hardware and software architecture
Also, when the micro IMU employed with the angular rate producer
with microelectromechanical system (MEMS) technology of the present
invention is functioned as a marine INS with embedded GPS, it has
the following unique features:
(1) Micro MEMS IMU AHRS with Embedded GPS
(2) Built-in CDU (Control Display Unit)
(3) Optional DGPS (Differential GPS)
(4) Flexible Hardware and Software System Architecture
(5) Low Cost, Light Weight, High Reliability
Again, when the micro IMU employed with the angular rate producer
with microelectromechanical system (MEMS) technology of the present
invention enables that the core micro IMU is used in a micro
pointing and stabilization mechanism, it has the following unique
features:
(1) Micro MEMS IMU AHRS utilized for platform stabilization.
(2) MEMS IMU integrated with the electrical and mechanical design
of the pointing and stabilization mechanism.
(3) Vehicle motion, vibration, and other interference cancelled by
a stabilized platform.
(4) Variable pointing angle for tracker implementations.
(5) Micro MEMS IMU utilized for a micro fire control system for
sniper rifles.
(6) Typical applications: miniature antenna pointing and tracking
control, laser beam pointing for optical conmmunications,
telescopic pointing for imaging, airborne laser pointing control
for targeting, vehicle control and guidance.
In view of above, the present invention can be used as a motion
measurement device for both commercial and government systems
required by phased array antenna systems for communication
on-the-move. Specific applications include pointing control systems
for mobile satellite reception for truckers and radiotelephone and
direct broadcast satellite reception. The development of a low cost
attitude and heading reference system is critical to wide
deployment of these systems in the commercial arena.
The present invention will be described as it applies to its
preferred embodiment. It is not intended that the present invention
be limited to the described embodiment. It is intended that the
invention covers all alternatives, modifications, and equivalencies
which may be included within the spirit and scope of the
invention.
* * * * *